Without limiting the scope of the disclosure, its background is described in connection with 3-D printing/additive manufacturing and with fiber-reinforced composites.
Additive manufacturing (AM, a.k.a. 3-D printing) has demonstrated itself to be highly capable of fabricating models, prototypes, tooling, and end-use parts. AM technologies such as stereolithography [Hull, 1986], selective laser sintering (SLS), and the POLYJET™ process of Stratasys typically build objects one layer at a time using a variety of processes and materials, including polymers. AM offers high geometric complexity, rapid time-to-market, the elimination of tooling and most programming, multi-material parts, and other benefits. However, the strength and stiffness of polymer AM parts is not high, and the opportunity exists to increase both strength and stiffness of AM parts if reinforcing fibers could be integrated into the printed structure. Other work [Mark, 2014 #1 and 2014 #2] has described methods for incorporating reinforcing fibers into or between layers of a part produced using AM, specifically using a modified fused deposition modeling (FDM) process. While the strength and stiffness of parts may be increased with such methods, this is true primarily within the plane of the layers, and not along the axis perpendicular to them; i.e., the resulting parts are highly anisotropic in mechanical properties. Moreover, with many AM processes such as stereolithography, supports made from the same material as the part are needed during the building process, which can be time-consuming and difficult to remove.
In the field of fiber-reinforced composites, it is difficult to obtain isotropic properties: typically, parts are weaker in the direction across the fiber laminations, for example, and stiffness also varies anisotropically. Composites remain fairly costly, in part due to their fabrication being labor-intensive or requiring complex, costly robotic machinery and often custom tooling. Also, the geometrical complexity available to composite parts is limited: certainly greatly so when compared to parts typically made with AM. It is also difficult to produce parts graded in properties.